Effect of self-interference flow of melt in cavity on the oritention of injection-molded polypropylene samples

The self-interference flow (SIF) in the cavity can be formed by two streams of melt flow injected through a new type mold gate, which consists of two orifices sharing with the same runner, the two streams of melt are superposed in the direction parallel to injection, and collide with each other in the direction perpendicular to injection leading to a crosswise flowing. The interactions between the two streams of flow undoubtedly have an influence on the morphology of the solid state. The effect of SIF on orientation degree of injection molded polypropylene (PP) samples was investigated. The macromolecular chain orientation in the amorphous state of SIF and CFP (conventional flow process) PP samples was tested by the use of a heat-shrinkage method. The results showed that the chain orientation degree in the SIF samples was lower than that in the CFP one. Transmission X-ray diffraction analysis showed that high crystal orientation occured in the shear layer for both samples, and the SIF sample exhibited a lower orientation degree of the crystal (040) planes as compared with the CFP sample.